Two Eastern black-and-white colobus monkeys were born at the Stone Zoo in Stoneham last week, marking the first successful birth of the species at the zoo in 25 years. The babies were first put on exhibit on Tuesday for the public.

The last group of monkeys maintained at the zoo were exclusively male and older. The recent addition of two young females and a male made breeding possible again.

“The births of the colobus monkeys present a wonderful opportunity for visitors to not only learn more about these fascinating animals, but to watch the babies grow up,” Zoo New England president John Linehan said Wednesday in a prepared statement.

The baby monkeys have not been named and their gender has not yet been determined, zoo officials said.

Zoo New England, which manages the Stone Zoo, participates in a national program dedicated toward promoting the survival of the colobus monkey.

Colobus monkeys are native to the forests of equatorial Africa and live in territorial groups run by a patriarch.

They usually spend most of the day sleeping in trees and exploring.

The newborn monkeys will be on exhibit during normal zoo hours, weather permitting, Linehan said.

“With the newborns in the group, we will probably be more conservative with rain or chilly temperatures,” Linehan said.